Gender differences exist in the neuroendocrine control of GH secretion in the human and experimental animals. The regulatory mechanisms that drive such sex differences are not known, but presumptively are estrogen dependent. We plan to study GH response to a synthetic secretagogue GHRP-2 in postmenopausal woman on and off estrogen. Novel insights into the specific neuroendocrine mechanisms of estrogen action will help explicate the physiological coupling between sex-steriods and the GH axis in health and disease.